An exclusive table lock prevents any other transaction from accessing the table for any operation (reads, writes, schema modifications, and so on). Only one transaction can hold an exclusive lock on any table at one time. Exclusive table locks conflict with all other table and row locks. However, unlike an exclusive schema lock, transactions executing at isolation level 0 can still read the rows in a table whose table lock is held exclusively.
You can acquire an exclusive table lock explicitly by using of the LOCK TABLE...IN EXCLUSIVE MODE statement. The REFRESH MATERIALIZED VIEW and REFRESH TEXT INDEX statements also provide a WITH EXCLUSIVE MODE clause that you can use to create exclusive table locks on the underlying tables while the refresh operation takes place.
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